This proposal is designed to study the neural coding of taste by learning about the circuitry of the first central synapse of taste-related nerves, the nucleus of the solitary tract (NTS). How the brain encodes taste is important because the coding mechanisms that are used by the taste system may also apply to other sensory systems. In addition, because of the link between taste and ingestion, the study of the taste system may provide insight into the etiology and/or treatment of eating disorders. Recent behavioral studies have suggested that the chorda tympani (CT) and the glossopharyngeal (GP), which innervate taste buds on the rostral 2/3 and caudal 1/3 of the tongue respectively, serve different functions in taste coding. At the present time, however, a description of the underlying circuitry in the central nervous system and of the functional interactions that support such a hypothesis is lacking. The long-term objective of the present proposal is to provide a description of the interaction of inputs onto taste cells in the NTS and the relationships of these inputs to the projection patterns of NTS cells. The specific aims are: 1) Evoked responses from electrical stimulation of the CT and GP nerves will be recorded in NTS cells and correlated with patterns of taste sensitivity. First, this experiment will test the hypothesis that the respective sensitivity patterns of the CT and GP nerves are conserved in the response profiles in NTS cells. Second, based on several suggestions in the literature, the hypothesis that input from the CT nerve inhibits input from the GP nerve will be tested using paired pulse electrical stimulation. 2) Evoked responses from electrical stimulation of the CT and GP nerve will be recorded in NTS cells, as well as evoked responses from electrical stimulation of the parabrachial nucleus of the pons (PbN), the second synapse in the ascending gustatory pathway. This experiment will test the hypothesis that the response profiles of NTS-PbN relay cells reflect parallel processing of taste stimuli by NTS cells receiving either CT or GP input. 3) Evoked responses from electrical stimulation of the CT and GP nerves and the gustatory neocortex (GN) will be recorded will be recorded in NTS cells. Taste responses in these cells will also be recorded before and after anesthetization of the ipsilateral and contralateral GN. This experiment will test the hypothesis that descending input from the GN differentially affects those cells that receive CT and GP input. By describing the taste responsivity of inputs and outputs of NTS cells, data from this project will help provide an understanding of information processing in the NTS.